The invention relates to a method of a boosted brake system of a vehicle. Furthermore, the invention relates to a control device for a boosted brake system of a vehicle.
In order to permit a driver of a vehicle to comfortably activate an activation element of a brake system, such as for example a brake pedal, a brake system generally has a brake booster. The brake system with a brake booster is often referred to as a boosted brake system.
A brake booster is configured to make available an assistance force which, in addition to a driver braking force applied to the activation element by the driver, causes at least one wheel to be braked. Suitable brake boosters are described, for example, in DE 10 2005 024 577 A1, DE 10057 557 A1 and DE 103 27 553 A1.
FIGS. 1A and B show schematic illustrations explaining a method of functioning of a conventional brake booster.
The brake system represented partially schematically in FIG. 1A has an activation element 10 which is embodied, for example, as a brake pedal. By activating the activation element 10, the driver can apply a driver braking force Ff and a first adjustment travel s1 to a transmitting component of the brake system, for example to an input piston 12 (see equivalent circuit diagram in FIG. 1B). In addition, the driver braking force Ff can be sensed by means of an activation element sensor system (not included in the sketch). The activation element sensor system comprises, for example, a force sensor for measuring the driver braking force Ff and/or a travel sensor for determining the first adjustment travel s1 of an adjustable component of the activation element 10.
The brake system additionally has a brake booster 14. The brake booster 14 is configured to make available an assistance force Fu so that the driver does not have to completely provide the force, as a driver braking force Ff, which is required to brake his vehicle. The assistance force Fu which is made available by the brake booster 14 can be, for example, a function of the driver braking force Ff.
The activation element 10 and the brake booster 14 are therefore arranged in the brake system in such a way that at least the driver braking force Ff and the assistance force Fu give rise to an overall braking force Fg. However, the overall braking force Fg can still comprise at least one further force. For example, the brake booster 14 transmits the assistance force Fu and a second adjustment travel s2 to an assistance piston 16 which is coupled, together with the input piston 12, to a coupling element, such as the reaction plate 18 which is shown. In the equivalent circuit diagram in FIG. 1B, the input piston 12 acts on a first point P1, and the assistance piston 16 acts on a second point P2, on the reaction plate 18. As a person skilled in the art knows, the points P1 and P2 can correspond to surfaces. For example, the point P2 corresponds to an annular surface in the case of a tubular assistance piston 16.
In this way, the overall braking force Fg and a third adjustment travel s3 can be transmitted to a component, such as for example the output piston 20, which is arranged on the outside of the coupling element. In this case, the output piston 20 is in contact with the reaction plate 18 at a third point P3, or at a corresponding one.
A quotient x gives the ratio of a first distance between the points P2 and P3 and of a second distance between the points P3 and P1. In the case of an elastic reaction plate 18, the latter is deformed in the case of a driver braking force Ff≠0 and/or an assistance force Fu≠0 (not illustrated in FIG. 1B). The bendability of the reaction plate 18 can be given as elasticity e.
The output piston 20 is coupled to an adjustable component 21 of a force/pressure conversion element, for example of a master brake cylinder 22. A brake circuit (not included in the sketch) which is filled with a braking medium and which has at least one wheel brake cylinder is connected to the force/pressure conversion element. The at least one assigned wheel can be braked by changing a brake pressure in the at least one wheel brake cylinder.
However, the operation of a conventional brake booster entails multiple disadvantages. For example, making available an assistance force Fu≠0 when the vehicle is in a stationary state and/or in the case of activation of a further additional braking torque which acts, in addition to the overall braking torque made available via the overall braking force Fg, on at least one of the wheels of the vehicle, generally leads to unnecessary energy consumption by the brake system. Furthermore, vibration of the third adjustment travel s3, for example in the event of operation of a pump of the brake system, brings about corresponding vibration of the first adjustment travel s1 owing to the bendability of the coupling element. The associated movement of the activation element is frequently irritating to the driver. It is therefore desirable to have a boosted brake system with a reduced energy consumption and/or an improved operator control comfort when activating the activation element.